light where it is efficient in an ellipsoidal reflector. At 575 watts, HPL lamps can produce as much light as an older 1000 watt lamp. Source Four is named for the HPL, its light source, having four filaments. It is also available in 375 W and 750 W versions, at a variety of rated supply voltages. HPL lamps are also available in longer-life versions that reduce the color temperature from 3250 K to 3050 K to give the lamp a life of around 1500–2000 hours as opposed to the 300-400 hour life of the standard HPL. Other versions ETC also manufactures a high-intensity discharge (HID) Source Four body with a metal-halide lamp. The fixture has a small box attached to the yoke of the fixture which contains the ballast and other additional control gear required to strike and operate an HID lamp. HID lamps are not dimmable. The HID fixture uses less energy than the standard HPL lamp. A range of Source Four instruments using LEDs are also available. The shutter, barrel, and lens tubes are identical to the HID and tungsten versions of the Source Four. Control of parameters such as color and light intensity is available via DMX. The power usage is approximately 25% of that of the equivalent tungsten version, although the purchase cost is significantly higher. Lamp life is significantly higher, retaining 70% of its original intensity at 50,000 hours. Barrel The Source Four is the first fixture to feature a rotating shutter barrel, which makes framing objects much easier regardless of lamp orientation. In previous fixtures, the shutters had only a limited range of motion and could not be rotated. The shutters are made from stainless steel, which does not warp as easily under the heat of the lamp. The shutters are arranged in 3 planes, allowing a degree of freedom in shutter placement by the extreme angles they can be racked to. The top and bottom shutters are on their own plane, with the 2 side shutters sharing a single plane. ETC also offers a variety of interchangeable lens tubes with various field angles. These are: 90, 70, 50, 36, 26, 19, 14, 10, and 5 degree lens tubes, some of which are available as enhanced definition lens tubes (EDLT). The Source Four is also available as a zoom fixture, with a non-interchangeable lens tube. According to ETC's manual, the lenses in each lens